High-voltage system



Feb. 20, 1951 D, W, EPSTEIN ET AL 2,542,493

HIGH-VOLTAGE SYSTEM Filed July 2l, 1949 2 Sheets-Sheet l afer/90N 60N Q 4 /A/vf/vm/Ps sa@ Dfw/0 M4 505mm No Feb. 20, 1951 D. W. EPSTEIN ET AL 2,542,493

` HIGH-VOLTAGE SYSTEM Filed July 21, 1949 2 Sheets-Sheet 2 omfcr/ l S/G'NL @fn/mam DAV/D Ml 5557501/ HND FRfDm/K/-l /V/UULL Patented Feb. 20, 1951 HIGH-VOLTAGE SYSTEM David W. Epstein and Frederick H. N icoll, Princeton, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application July 21, 1949, Serial N0. 105,924

23 Claims.

The present invention relates to improvements in high voltage systems and more particularly to improvements in voltage generating circuits suitable for producing relatively high unidirectional potentials for use as electron discharge tube polarizing potentials.

In still more particularity, the present invention concerns itself with improvements in high voltage generating apparatus for use in connection with cathode ray tubes requiring beam accelerating potentials of a magnitude promoting undesirable losses in the form of corona discharge especially under low atmospheric pressure conditions.

Advances in the ield of electronics during the last decade or so have brought about the need for, more compact, reliable, efficient and safe means for developing relatively high potentials upwards of several thousand volts gor more for application in devices finding common use in the art and by the public. Y

'Ihis need for improved high voltage generation isA perhaps no better deiined than in that branch of electronics dealing with electronHV beam apparatus. For instance in radar, teleran, television, oscillographic test equipments, etc., use is frequently made of cathode ray equipment requiring unidirectional beam accelerating f potentials of considerable magnitude. In theioast, it has `been the practice to provide means for developing such potentials by rectiiication of high amplitude voltage pulses, RF type power supply units, high frequency vibrator packs, and rather straightforward power line frequency voltage step-up and doubling methods. A11 of these systems require the use of well-insulated transformer windings, well-constructed voltage rectiers for handling high peak potentials, and careful physical layout of the power supply wiring. This latter requirement becomes increasingly important as the magnitude of the voltage increases since corona discharge losses become proportionally more diilicult to control. Moreover, as the operating potential is increased, the personnel shock hazard is also increased, thereby demanding rather elaborate and costly shock prevention arrangements in order to insure adequate equipment operating safety.

The problems associated with high voltage systems such as, for example, arc-over and crona discharge are even more pronounced under conditions of reduced atmospheric pressure as brought about in the operation of airborne electronic gear. Properly designed high voltage systems, for example, suitable for supplying beam accelerating energy to a radar viewing tube at sea level could conceivably fail in operation at altitudes even as low as ten or twenty thousand feet.

It is therefore a purpose of the present invention to provide an improved system for developing high unidirectional potentials for use in connection with high vacuum electron discharge devices.

It is another purpose of the present invention to provide a new and improved arrangement for high voltage generating equipment used for the development of beam accelerating potentials for cathode ray devices.

Another object of the present invention resides in a high voltage power supply arrangement for use in connection with cathode ray tube equipments which measurably reduces corona discharge losses.

Another object of the present invention is to provide an improved form of high voltage power supply layout for use in supplying biasing potentials for vacuum electron discharge devices such as to permit successful operation of such devices and the equipment with which. they are associated under conditions of reduced atmospheric pressure without suffering undesirable insulation breakdown and corona losses.

A still further object of the present invention is to provide a novel form of cathode ray tube construction which confines the generation of necessary high magnitude beam accelerating potentials to the vacuum chamber of the cathode ray tube proper thereby eliminating personnel shock hazards and rather elaborate and costly corona discharge control measures.

In one of its more general concepts, the present invention contemplates the use of an excitable alternating current voltage generating means and incorporated in the tube envelope of the discharge tube to which the high unidirectional potential is to be applied. Within the discharge tube envelope is also provided means for rectifying the high alternating voltage produced by the excitable voltage generating means, the output of the rectifier being connected with the tube structure requiring the high unidirectional potential. Suitable means is then positioned on the outside of the tube envelope in exciting relationship with the voltage generating means within the envelope, the exciting means being designed for operation at easily obtained and controlled operating potentials offering substantially little shock hazard to personnel.

In one of its more speciiic forms, the present invention applied, for example, to a cathode ray kinescope requiring beam accelerating potentials of several thousand volts or more, contemplates the use of a high voltage coil member located within the kinescope envelope. Integral with the kinescope tube structure is then placed a simple diode rectifier, in some instances having its electrodes exposed to the evacuated atmosphere of the envelope interior. A suitable filtering network may then be incorporated adjacent the diode structure to form an overall rectifying means whose output is connected with the beam accelerating electrode of the kinescope. The high voltage coil member may then be electromagnetically excited from outside the kinescope envelope by means of a driving coil connected with some source of relatively low potential alternating current power. Thus, the actual voltage applied to the kinescope accelerating electrode is not exposed to the outer atmosphere and hence reduces the possibility of corona discharge and injurious encounter by operating personnel,

Other objects and advantages will be apparent from the following description of the invention when considered in connection with the accompanying drawings in which:

Figure 1 shows one form of the present invention applied to a cathode ray tube of the electromagnetic deflection variety;

Figure 2 shows another form of the present invention applied to a cathode ray tube of the electromagnetic :deflection variety;

Figure 3 shows the present invention applied to a cathode ray tube of the electrostatic deflection variety in which the developed high voltage is used as second anode potential;

Figure 4 shows still further embodiment of the present invention as applied to a cathode ray tube wherein the developed beam accelerating potential energy is derived from a beam deflection circuit.

Turning now to Figure l, there is shown at I8 an envelope having a neck portion l2 and a target portion Il! for containing a cathode ray tube assembly such as, for example, an image reproducing kinescope. An electron gun at I6 produces a beam of electrons shown in dotted lines at I8, which beam is desirably accelerated by application of a high positive accelerating potential to the metal shield 28 (sometimes referred to as a beam accelerating electrode) This shield may be connected with the neck conductive coating 2l by means of wire conductors or spring contacts. As pointed out hereinabove, prior art systems, in providing the accelerating electrode with the high unidirectional accelerating potential, have generally developed the high voltage external to the envelope I and applied this voltage to the accelerating electrode 2i! by means of a connection to the electrode brought through the walls of the envelope l0. As noted this has resulted, especially at high altitudes, in occasion for high corona discharge losses, as well as irnpending danger to operating personnel.

According to the present invention, a high voltage coil member 22 is situated within the envelope l0, one end of the coil 22 being brought to ground potential through a seal 24 in the envelope. External to the envelope I8 is then placed a driver winding 26 magnetically coupled, as shown by the dotted flux lines 28, to the high voltage winding 22. The driver winding 26 may be connected with any suitable source of alternating power for inducing a voltage in the high voltage Winding 22. In the arrangement shown, the driver winding 26 is connected in the anode circuit of an oscillator tube 30, A tickler wind- 4 ing 32, properly phased and applied between the grid 3l! and cathode 36 of the tube 30, then provides a self-sustained oscillation of the vacuum tube, whose frequency is controllable by the variable capacitor 38.

Situated, also in accordance with the present invention, within the envelope il! is a rectifying device such as, for example, the diode 48 having an anode d2, cathode M, and heater 36. The upper extremity of the high voltage winding 22 is then connected to the anode c2 of the diode 40 so that alternating voltage'appearing across the winding will be rectified to develop a high unidirectional potential across the storage capacitor 48. The voltage thereby appearing across the capacitor 48 is connected directly to the accelerating electrode 28 of the cathode ray tube. Heater current for the diode 4Q may be conveniently obtained by providing an additional winding 50 magnetically coupled to the driver winding 26 and connected across the heater 6.

Operation of the arrangement shown in Figure l, in accordance with the present invention, will be seen to be rather straight-forward. The oscillator stage, incorporating the vacuum tube 3D, producing a variable magnetic iux by means of driver winding 26, will induce in the high voltage winding 22 a high voltage alternating current whose magnitude is a function of the turns ratio between the coil member 22 and the driver winding 25. This alternating voltage is then rectified by the diode 48 and applied as described to the accelerating electrode 28. The metallic shield either solid or porous not only serves as an accelerating electrode for the gun structure but also tends to prevent ux from the pick up coils from adversely influencing the beam.

Another convenient form of the present invention is shown in Figure 2 where the high voltage coil member 22a not only surrounds the electron beam I8, but the driver winding 26a and tickler winding 32a are also brought within the envelope I0 and oriented with their axes in alignment with the high voltage coil member 22a. In this instance, a simple diode structure such as 52 having an anode 54 and heater 56 may be employed such that the heater pick up coil 53, used for exciting the heater 5B need only be a small turn not necessarily surrounding the metal shield. This makes the construction of the diode 52 rather simple and permits the supporting members for the heater 55 to actually constitute the heater pick up coil 53. As shown in both Figures l and 2, conventional delection coils, such as 68 and 68a, as well as focussing coils 62 and. 62a, may be used for electromagnetic control of the electron beam i8. It will be noticed that the arrangement of Figure 2, although requiring no driving coil outside of the tube envelope, does require a plurality oi seals at Sli for communicating the coil termini to the oscillator vacuum tube 38a.

The arrangement of Figure 3 depicts another form of the present invention as applied to electrostatic deflection type of cathode ray tube. Here within the neck portion 65 of the envelope 68 are placed the high voltage coil member 26D and driver winding 32h magnetically coupled with one another and substantially concentric with the axis of the cathode ray gun 18. A heater voltage pick up winding 10 is also provided for excitation of the heater 'H (shown in dotted lines) of the cathode ray gun. Storage capacitor 16 is conventionally connected in storage relationship with the output of rectier 14. In the particular embodiment shown, the heater of the rectier 'I4 is connected with the anode T9 of the electrostatically focussed electron beam gun 18, the beam 8B of which is deflected by electrostatic deflection plate sets 82 and 841. The anode I9 is then grounded through the conductive coatn ing 69 inside the tube, the coating itself being grounded through the seal at S5. The high voltage coil member 2Gb is accordingly connected from the anode of diode 'I4 to the cathode 'i3 of the cathode ray gun whereby to establish the cathode i3 at a high negative unidirectional potential with respect to the anode i9. It is for this reason that the gun heater 'il is preferably heated by the coil i9, Storage capacitor 'I6 and bleeder resistor 83 are connected directly across the output of the rectier appearing between the anode 'i9 and cathode '13. A tap on the bleeder 83 provides a suitable voltage for application to the focussing electrode 9| located between the two sections of the anode.

As indicated in Figure 3, the driver winding 32h need not necessarily be associated with an oscillator as in Figures 1 and 2, but may receive alternating current energy from a steep wave front generator, such as Sii, productive of a pulse waveform such as Eil or any other suitable waveform, such as a square wave, having rapid rise and fall contour characteristics. Also, no truly high potential beam` accelerating energy is necessarily required in the arrangement of Figure 3. Thus, the present invention is shown to be useful in generating even the relatively low beam influencing potentials required by the electrostatic type gun i8. Although such voltages are usually lower than required by high velocity beam accelerating arrangements, its development by conventional methods may still present considerable problems especially at high altitudes. The leads to the diode heater 'l2 may be brought through the tube envelope and heated from an external source (such provision being shown in Figure 3) or the heater may be energized from a separate heater energization winding on the same basis as the cathode ray gun heater.

A still further adaptation of the present invention to a cathode ray electron discharge tube is illustrated in Figure 4 where the high voltage coil member 26o is oriented such as to actually surround the electron gun assembly 88. The neck po-rtion 9D of the cathode ray tube envelope 92 may be slightly enlarged to accommodate this positioning of the coil member 28C. The material in the vicinity of coil member 26e from which the tube envelope is made is preferably highly permeable to magnetic ilux such as, for example, glass. The driving coil 32e may then be placed concentric with the normal portion 90a of the neck 90, outside the tube envelope and thereby provide flux linkages with the high voltage coil member 29C. As shown, the diode 94, positioned within the envelope neck 9S, has its anode 96 connected with the high voltage terminal of the coil member 29e so as to develop at its filament 98, a high unidirectional potential which is applied to the conductive coat |99 leading to the beam accelerating electrode of the cathode ray tube. Suitable excitation of the filament 98 may be obtained from an auxiliary winding |02 also concentric with the electron gun structure and in magnetic coupling relationship with the driver coil 32e.

A convenient form of providing excitation to the driver winding 32e is shown in the embodilill ment of Figure 4. This form is especially suited to application in television receivers where, in order to establish minimum circuit cost, absolute reduction in circuit necessary components is desirable. Here the deflection output tube IM, driven by the deflection signal generator I 05, has directly included in its anode-cathode circuit, the driver winding 32e, as well as a deflection Winding, such as X-X of the deflection coil |98. A B boost damping arrangement comprising the diode H0, linearity inductance H2, and storage capacitor l M is shown in shunt with the winding X--X of the deiiection coil. This B boost damping arrangement is shown and described in more detail in a co-pending application by Simeon I. Tourshou, Serial No. 90,6i2 entitled Television Deection Power Recovery Circuit led April 30, 1949.

In the operation of the arrangement in Figure Zl, the current transient through the deflection winding X-X and driving winding 32e, produced during the deection lyback interval, causes a high peak voltage to be induced in the coil member 26o. As in the previous embodiment, the turns ratio between the coil member Ec and the driving member 32o is relatively large so that a high amplitude pulse representing the flyback transient will appear at the anode 9&5 of the diode 94 for rectication and application as accelerating potential to the accelerating electrode of the cathode ray tube.

In practice, it has been found that in order to minimize the adverse defocussing effects of the auxiliary windings, such as 29o and E92 as well as the driving Winding 32e, upon the beam produced by the electron gun 89, it is necessary to restrict the positioning of the coils to not more than l" to 11k in front of the cathode electrode 88u of the electron gun structure. Depending upon the exact conguration of the gun structure, this critical distance may vary somewhat.

It has been further found that care must be exercised in the choice of materials used in the construction of the coils residing in the evacuated chambers. This is necessary inasmuch as these coils must be subjected to the degassing temperatures required for processing and manufacturing the electron gun structure and tube. Any impurities in the wire insulation in making the coils within the envelope are likely to be volatilized or oxidized during the degassing process and result in contamination of the operating vacuum. In a co-pending U. S. application, Serial No. 102,092 entitled Method for Making Insulated Wire and Coils filed June 29, 1949 by Frederick H. Nicoll and David W. Epstein, such contamination is dealt with in more detail and a method for manufacturing coils suitable for this purpose is fully described.

Moreover, there has been found that the choice of dielectric for the storage capacitor, such as d (shown in Figures 1 and 2), 16 (shown in Figure 3) and H6 (shown in Figure 4) of the high voltage System disclosed by the present invention is also important since it too must withstand the high degassing temperatures of the tube structure. For this purpose, it has been found that barium titanate performs exceptionally well.

It will be understood by those skilled in the art that the present invention, although having been described in connection with cathode ray beam apparatus, is not limited in its utility thereto. Other applications, such as in electron amplifying tubes and other special purpose discharge tubes requiring high voltagepotentals, also lend themselves to the practice of the present invention. Furthermore, it will be understood that, although the rectifying diode shown in the various embodiments of the present invention as having its elements exposed to the atmosphere Within the tube envelope, it is Well within the scope of the present invention to place a conventional high voltage rectier tube having its own envelope within the evacuated chamber in the positions equivalent to those shown above. In some instances, it is desirable to replace the heater type diode with a cold cathode type rectifier which replacement eliminates the need of additional lament excitation winding illustrated in the above embodiments.

From the foregoing description of the present invention, it is manifest that its utility is in no way limited to the inclusion of only the highvoltage pick-up winding and associated rectifying device in the evacuated envelope. It is clear from Figures 1 and 2 that the driver tube 30 might well be included in the evacuated envelope of the cathode ray tube I0. Its elements may or may not accordingly be subjected to the atmosphere of the evacuated envelope, depending upon manufacturing conveniences. The present in- Vention also contemplates the use of a highvoltage pick-up winding and rectifying element inside an evacuated envelope for use in conjunction With a driver winding, such as 26 in Figure 1, wherein the high unidirectional potential thereby developed is used for any purpose within the envelope or brought out through the envelope for use at some other circuit arrangement. If, for any reason, it is desired to increase the coupling between the driver winding and the high-voltage pick-up coil in any of the arrangements shown, it is, of course, obvious that a ferrite core structure could be employed to more concentratedly direct the paths of flux linkage. For example, in Figure 4 a ferrite core might well be incorporated in the neck portion of the evacuated envelope so as to be axially concentric with the coils 26a and 32o, thus increasing the magnetic coupling therebetween and increasing the unidrectional voltage developed by the diode 94.

Having thus described my invention, what we claim is:

l. An electrical device comprising in combination, an evacuated envelope having a magnetically permeable area in its surface, an electromagnetic pick-up coil fixed within said envelope and positioned adjacent said envelope permeable area, rectifying means positioned within said envelope and connected with said pick-up coil for developing a unidirectional potential in accordance with alternating voltage induced in said pick-up coil, and means connected with said rectifying means for utilizing the develop-ed unidirectional potential.

2. An electrical device comprising in combination, an evacuated envelope having stationed therein an electronic vacuum tube assembly including an electrode requiring a unidirectional operating potential, said envelope having a, magnetically permeable area in its surface, an electromagnetic pick-up coil fixed within said envelope and positioned adjacent said envelope permeable area, rectifying means positioned within said envelope and connected with said pick-up coil for developing a unidirectional potential in accordance with alternating voltage induced in said pick-up coil, and connections from the output of said rectifying means to said vacuum tube assembly electrode requiring a unidirectional operating potential.

3. In an electrical device employing an evacuated envelope having a magnetically permeable area in its surface with unidirectional voltage utilization means situated within said envelope, the combination of: a high voltage electromagnetic pick-up coil within said evacuated envelope and adjacent the magnetically permeable area in the envelope surface, voltage rectifying means positioned within said envelope and connected with said pick-up coil such to develop a unidirectional potential in accordance with any alternating current energy induced therein, and connections applying the output of said voltage rectifying means to said unidirectional potential utilization means.

4. Apparatus according to claim 3 wherein said voltage rectifying means comprises a diode electron tube structure having a heater element and wherein there is additionally provided within said envelope a low voltage electromagnetic pick-up coil adjacent said rst pick-up coil, the output of said low-voltage pick-up coil being connected with said diode heater element for excitation thereof.

5. Apparatus according to claim 4 wherein the elements of said diode electron tube structure are maintained in and exposed to the atmosphere of the evacuated envelope interior.

6. In an electrical device employing an evacuated envelope with unidirectional potential utilization means situated within said envelope, the combination of, a high voltage coil member mounted within said evacuated envelope, means for producing a high potential low current alternating voltage in said coil from a relatively low potential high current power source situated outside said envelope, voltage rectifying means positioned within said envelope and connected with said high voltage pick-up coil such to develop a unidirectional potential from the high potential alternating voltage produced therein, and connections from the output or said voltage rectifying means to the unidirectional potential utilization means situated within said envelope.

'7. Apparatus according to claim 6 wherein said coil member high potential low current voltage producing means comprises magnetic coupling to a driver winding adjacent to and having fewer turns than said high voltage pick-up winding, said drivrr winding being adapted for connection to the low potential high current source.

8. Apparatus according to claim 7 wherein said voltage rectifying means comprises a diode electron tube structure whose elements are mounted in and exposed to the atmosphere of the envelope interior.

9. In a cathode ray beam apparatus employing an evacuated chamber having situated therein electron beam generating structure requiring a relatively high unidirectional beam influencing potential, the combination of: a high voltage coil member mounted within the chamber', means for electromagnetically inducing into said high-voltage coil member high potential low-current alternating voltage from a relatively low potential high-current power source located outside said chamber, voltage rectifying means positioned within said chamber and connected with said high-voltage coil member such to develop a relatively high unidirectional potential from the high potential alternating voltage produced in said coil membor, and connections applying the unidirectional potential output of said rectifying means to a portion of the beam generating apparatus requiring the beam influencing potential.

10. Apparatus according to claim 9 wherein said voltage rectifying means comprises a diode electron tube structure whose elements are mounted in and exposd to the evacuated atmosphere of the beam apparatus chamber interior.

l1. Apparatus according to claim 9 wherein the walls of said chamber have a magnetically permeable portion adjacent said high-voltage coil member and wherein said coil member electromagnetic voltage inducing means comprises a driver coil, of substantially fewer turns than said coil m-mber, positioned outside said chamber but adjacent said magnetically permeable wall portion thereof such to be in magnetic coupling with said high-voltage coil member.

12. Apparatus according to claim 11 wherein the axes of both said driver coil and said highvoltage coil member are in substantial alignment with the axis of the electron beam generating apparatus.

13. Apparatus according to claim 9 wherein said coil member electromagnetic voltage inducing means comprises a driver winding of substantially fewer turns than said coil member, said driver winding being positioned within said chamber and in magnetic coupling relati-onship with said coil member, the lead connections to said driver winding being vacuum sealed through the walls of said chamber for connective availability from without said chamber.

14. In a cathode ray beam tube having an evacuated chamber comprising a neck section and a target section, the neck section having situated therein a beam generating structure incorporating an electr-on emissive cathode, a heater for said cathode, while said target section having included therein a beam accelerating electrode requiring a relatively high unidirectional potential, the combination of: a high voltage coil member mounted within the target section of said chamber such that the coil axis is substantially in alignment with the extended axis of said beam generating structure, a driver winding within said chamber target section having its axis in alignment with said coil member and positioned for magnetic coupling therewith, connections outwardly available through the walls of said evacuated chamber for energizing said driver winding, a voltage rectifying means situ-ated within the chamber target section and connected with said high voltage coil member for producing a high unidirectional potential in accordance with alternating voltage induced therein by said driver winding, and connections from the output of said voltage rectifying means to the beam accelerating electrode in said target section.

15. Apparatus according to claim 14 wherein there is additionally provided a tickler winding magnetically coupled to said driver winding and said high voltage coil member, and connections through the walls of said evacuated chamber making available from without said chamber voltage pick-up induced in said tickler winding.

16. Apparatus according to claim l wherein there is additionally provided an electron vacuum tube oscillator circuit utilizing said tickler coil in its input circuit and said driver winding in its output circuit whereby energy developed by said oscillator circuit is transformed by said high voltage coil member and said rectifying means 10 to a high unidirectional beam accelerating potential.

17. In a cathode ray beam apparatus employing an evacuated chamber having a neck section and a target section, the neck section incorporating an electron beam generating structure including an electron emissive cathode while said target section incorporates abeam accelerating electrode demanding a high unidirectional potential, the evacuated chamber neck section having at least a portion thereof pervious to electromagnetic flux in combination, a high voltage coil member mounted within the evacuated chamber neck section adjacent the magnetically pervious portion thereof, voltage rectifying means positioned within said evacuated chamber and connected with said high voltage coil member such to rectify any alternating voltage induced in said coil member, and connections applying the output of said voltage rectifying means to the accelerating electrode in said evacuated chamber target section.

18. Apparatus according to claim 17 wherein said high voltage coil member surrounds a portion of said beam generating structure and is positioned not more than 11/2" from the beam generating structure electron emissive cathode in the direction of the evacuated chamber target section.

19. Apparatus according to claim 18 wherein there is additionally provided a driver winding positioned on the outer surface of a concentric with the neck portion of said evacuated chamber so as to be in magnetic coupling relationship with the high voltage coil member mounted within the chamber and connections applying said driver winding to the output circuit of an electromagnetic beam deflection driver stage whereby said beam accelerating for said cathode ray beam apparatus is derived from the electromagnetic beam deflection driver stage.

20. A cathode ray beam apparatus having an evacuated chamber which embraces an electron gun assembly and a beam accelerating electrode, an excitable alternating voltage means positioned within said chamber, lvoltage rectifying means connected with the output of said alternating voltage generating means for producing a high unidirectional potential, connections from the output of said voltage rectifying means to said beam accelerating electrode, and means for exciting said voltage generating means from outside said chamber.

21. In a cathode ray beam tube having an evacuated chamber comprising a neck section and a target section, the neck section having situated therein a beam generating structure incorporating an electron emissive cathode, a heater for said cathode, a beam forming an accelerating electrode structure with an associated focussing electrode for directing an electrode beam into the target section, the combination of, a high voltage coil member mounted within the neck section of the chamber such that the coil axis is substantially in alignment with the extended axis of said beam generating structure, a driver winding within said chamber having its axis in alignment with said high voltage coil member and positioned for magnetic coupling therewith, connections outwardly available through the walls of said evacuated chamber for energizing said driver winding, a voltage rectifying means situated Within the chamber and connected with said high voltage coil member for producing a high unidirectional potential in accordance with alternating voltage induced therein by said driver winding, said voltage rectifying means having a positive output terminal and a negative output terminal, connections from said Voltage rectifying means positive output terminal to said beam accelerating electrode structure, and connections from said voltage rectifying means negative output terminal to said electron emissive cathode.

22. Apparatus according to claim 21 wherein a bleeder resistance is connected across the output terminals of said voltage rectifying means within said evacuated chamber, said bleeder resistance having a tap intermediate between its extremities and wherein there is a connection from said bleeder tap to said cathode ray tube focussing electrode.

23. Apparatus according to claim 21 wherein there is additionally provided a heater pick-up 12 winding magnetically coupled with said driver winding, the output of said heater winding being connected with said beam generating structure heater for energization thereof.

DAVID W. EPSTEIN. FREDERICK H. NICOLL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,570,444 Mavrogenis Jan. 19, 1926 1,590,467 McCullough June 29, 1926 1,930,499 Zworykin Oct. 17, 1933 2,048,129 Loughridge July 21, 1936 2,436,393 Maggio Feb. 24, 1948 

